Check your engine aand transmission mounts. If one os loose it will let the engine move a little and the throttle rod moves when the engine does.
Had this problem on mine a while back and the drivers side transmission mount bolt had fallen out. Mine you would swear had kangaroo gas in it.
Oil on the clutch disc usually makes a clutch chatter on take off.
Another reason for "bucking" could be carburetor is out of adjustment.
